Drafting Standards

AHD means Australian Height Datum - the national vertical datum Australian drawings measure their RLs from, with zero at approximate mean sea level. What AHD means AHD is the Australian Height Datum - the national reference surface that Australian drawings measure heights from. When a drawing says RL 42.600 AHD, it means 42.600 m above that surface. AHD was adopted in … [Read more...] about What Does AHD Mean on a Drawing? Height Datum

O/A means overall — the dimension spans the full extent of the item, outside face to outside face, including frames, end plates, linings and projections. O/A is a hand-lettering habit that survived the move to CAD, and it is still all over Australian and UK drawings. It looks trivial until you realise it is one of three numbers describing the same object. What O/A … [Read more...] about What Does O/A Mean on a Drawing? (Overall)

RL means reduced level: the height of a point measured from the vertical datum the drawing nominates as zero, written in metres as RL 24.350. What RL means RL stands for reduced level. It is the height of a point measured vertically from whatever surface the drawing nominates as zero. The word "reduced" is a leftover from levelling fieldwork. A surveyor books staff … [Read more...] about What Does RL Mean on a Drawing? Reduced Level

CLR means clear — either a clear, unobstructed dimension between finished faces, or clear cover from a concrete face to the nearest reinforcing steel. CLR does two different jobs on a drawing set, and both are numbers people build to. Work out which you are reading. Meaning 1: a clear dimension It is measured between the faces of the two things named, with nothing … [Read more...] about What Does CLR Mean on a Drawing? (Clear)

TYP means typical — the dimension, detail or note it tags applies to every similar condition, not just the one the leader line happens to point at. TYP is one of the hardest-working abbreviations on a drawing set, and one of the most argued about. It is not hard to understand. The trouble is always in the extent. What TYP means TYP means typical. It converts a single … [Read more...] about What Does TYP Mean on a Drawing? (Typical)

NTS means not to scale — the view it labels is drawn for clarity rather than proportion, so you read the figured dimensions instead of measuring off the sheet. NTS turns up under a detail title where a scale should be. Here is what it is telling you to do. What NTS means NTS means not to scale. The view it labels is not a true proportional reduction of the real thing, … [Read more...] about What Does NTS Mean on a Drawing? (Not to Scale)